The present invention relates to a rotary electric machine and, more particularly, to a pole change type motor with armature coils allowing the change of the number of poles.
In machine tool feeders, cargo gears, etc., for the purpose of improving an accuracy of the stopping position and of mitigating the shock at the stop of the drive mechanism, the rotating speed is first dropped from high to low, then the brake is applied. The method for making use of the regenerative braking of the induction motor, which is caused when its speed changes from high to low, has frequently been employed. To these purposes, a method using a pole change type motor, which is capable of changing the number of rotations of the drive motor by two or more steps, or two or more motors with different poles has been used.
The method using two motors with different number of poles not only needs an increased area for their installation but also are expensive. In the case of using the pole change type motor, a large speed ratio such as 1:4 or 1:8 is required. For this reason, different windings which provide different poles are applied for a single armature. For example, when the number of rotations for two-pole and twenty-pole windings are required, the two-pole and twenty-pole windings are applied for a single armature core. In operation, when the motor is operated in a two-pole mode, the twenty-pole windings are not used, while when the twenty-pole windings are used, the two-pole windings are not used.
In this approach, however, the armature windings are inefficiently used and the size of the armature core is large, thus hindering the miniaturization of the motor.